This is Vulkan 1.1's "preferred method of line rasterization, and must
be used when the implementation advertises the strictLines limit in
VkPhysicalDeviceLimits as VK_TRUE."

The 'Diamond test convention' code path, which implemented coverage
corresponding to the Bresenham algorithm (except for endpoints, see
b/80135519), is now inactive, but might become of use again for
implementing VK_LINE_RASTERIZATION_MODE_BRESENHAM_EXT so it is kept,
for now.

Bug: b/139755234
Tests: dEQP-VK.*line*
Change-Id: I0113c04e35c1aca8031194223e589962942e18fa
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/35308Reviewed-by: Chris Forbes <chrisforbes@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>